Surface mounted (SMT) integrated circuit devices are fast becoming the dominant type of IC packaging in the electronics industry. These devices come in a wide variety of package configurations and lead pitch geometries. For example, IC packages may be square or rectangular with electrical contact or lead counts from 44 to 232 or higher. A variety of electrical contact or lead types are also being used. Quad flat pack IC's use Gull wing leads or J-leads. Both type of leads extend from the perimeter of the IC package with the former type of leads bending down and outward from the package while the later bend down and fold under the package in a J-shape. The leads are soldered to electrical contact pads formed on a circuit board.
The small pitch geometries of the quad flat pack SMT devices makes these devices very difficult to probe using oscilloscope or logic analyzer probes. The pitch geometries or lead spacing between lead centers varies on these devices. The most commonly used lead spacings for quad flat packs are 0.5 mm, 0.65 mm, 0.8 mm, 1 mm, 0.025 inches and 0.019 inches. Work is progressing on even smaller pitch geometries in the range of 0.010 inch lead spacing. The standards for gap spacing between leads is set out in JEDEC Publication No. 95, MO-104 and varies for the various lead spacings. For example, the minimum gap spacing standard for an 0.025 inch pitch geometry is 0.010 inches and 0.008 inches for a 0.019 inch pitch geometry. Using oscilloscope probes on these types of IC packages can cause the shorting of adjacent leads of the device.
U.S. Pat. No. 5,184,065, assigned to the assignees of the present invention, describes a twist lock probe tip for use with passive measurement probes. The probe tip has a flat flexible body of insulating material with an electrical conductor embedded or coated on one or both sides of the body. The flexible body has a notch or notches for exposing the embedded electrical conductor and/or for engaging a lead of an electronic component. The flexible body is inserted between the leads of the electronic device and twisted by means of an attached knob or wing lever so that the notches engage adjacent leads and the conductor or conductors contacts the desired lead or leads. As the pitch geometries of electronic devices continue to decrease, the leads on the electronic devices become increasing fragile and susceptible to bending and damage. Further, the chance for shorting adjacent leads together by bending leads increases as the gap between leads decreases. The twist lock probe tip design has the potential for deforming the leads of the electronic device as the probe tip is twisted into position. Additionally, the probe tip becomes increasing fragile as the thickness of the tip is decreased to match the decreasing gap size of the leads, especially where the notches are added for locking the tip between the leads. Further, the thickness of the tip may exceed the leads gaps, especially where electrical conductors are formed on opposite sides of the insulating material.
U.S. Pat. No. 5,387,872, assigned to the assignees of the present invention, describes a positioning aid for directly positioning a hand-held electrical test probe onto leads of a surface mounted integrated circuit device. The positioning aid has a housing made of a polycarbonate material with a central bore therethrough for receiving the probing tip of the test probe. One end of the housing that is normal to the bore has at least four teeth extending therefrom defining slots for engaging the leads of the integrated circuit device. The central bore is exposed in the central slot for exposing the probing tip therein for providing an electrical connection between one of the leads on the integrated circuit device and electrical circuitry in the test probe.
The usefulness of this design is limited by the thickness of the teeth. For pitch geometries less than 0.019 inches, the teeth become to fragile for practical use due to the thickness of the teeth being so small. Further, this design does not lend itself for dual lead probing where adjacent IC leads are probed using a single probe. Modifying this design for such a use requires some sort of internal transition from the pitch spacing of the probe contacts to the pitch spacing of the IC leads. Such a transition is considered expensive and increase the manufacturing costs of such a device.
U.S. Pat. No. 5,506,515 describes a high-frequency probe tip assembly for low-loss microwave frequency operations. The tip assembly includes a semi-rigid coaxial cable that is formed with a semicylindrical recess defining a shelf along which an inner finger and outer pair of fingers are mounted. Each finger is made of a resilient conductive material, such as beryllium copper, so as to form a coplanar transmission line. Cantilevered portions of the fingers extend past the end of the cable to form an air-dielectric transmission path of uniform and stable characteristics. The inner finger is electrically connected to the central conductor of the semi-rigid coaxial cable and the outer pair are electrically coupled to the shield of the semirigid cable.
The probe tip is designed as part of a coaxial transmission line for probing pads of integrated circuit dies. As such, the fingers of the probe tip need to be configured in terms of material composition, cross-sectional geometry and spacial orientation to provide a uniform deflection characteristic relative to each finger for even wearing of the pads and fingers and for stability of transmission characteristics despite contact pressure variations. These requirements result in the use of rigid conductive material for the fingers. Additionally, the design does not require the use of insulating material other than the air gaps between the fingers. Further, this design does lend itself for use with standard electrical measurement probes, such as used in conjunction with oscilloscopes, logic analyzers, and the like.
What is needed is a probe adapter for electrical measurement probes that are used in conjunction with oscilloscopes, logic analyzers, and the like for probing closely spaced leads of an electronic device, such as a surface mounted integrated circuit IC. The probe adapter should have electrically conductive elements that are compatible with the pitch geometry of the IC leads and electrical contacts compatible with the pitch geometry of the measurement test probe.